Conventional single-rod measuring chains include, essentially, two concentric glass cylinders, which are joined together at a first axial end section by melting, wherein the inner cylinder has at the first end section, usually, a pH glass-membrane and is filled with a buffer, the annular chamber between the inner and the outer cylinder contains the KCl-solution, and the outer cylinder has in the first axial end section or in a section axially adjoining such, a porous diaphragm, through which an electrolyte bridge to the surrounding, measured medium is produced. Both from the inner cylinder as well as from the annular chamber, metal conductors extend, for providing access to, respectively, the pH-potential and the reference potential.
A structural requirement is to provide sealed closure of the annular chamber and the inner cylinder at a second axial end section lying opposite to the first axial end section, without interfering with the accessing of the potentials. The sealing of the closure must, in such case, be assured, both at high temperatures, for example, >130° C. during autoclaving, as well as also at high pressures, for example, up to about 16 bar or more.
Conventionally, wires, as metal conductors, are bonded into glass for sealing, by melting of the glass, or they are held adhesively by potting in feed-throughs in more or less suitable materials. These feed-throughs leave the manufacturing process successfully sealed only after the expenditure of considerable effort.